Process for producing cold by solid-gas reaction and device pertaining thereto

ABSTRACT

A device for producing cold between +10° C. and -40° C., particularly in transport vehicles comprises at least one reactor (R), a condenser (C), a gas collector (Co) and an evaporator (E). The following simultaneous reactions are produced in the reactor (R): ##EQU1## the symbols &lt; &gt;; [ ] and ( ) denoting the solid, liquid and gaseous states respectively, X being chosen from ZnCl 2 , CuSO 4 , CuCl, LiBr, LiCl, ZnSO 4 , SrCl 2 , MnCl 2 , FeCl 2 , MgCl 2 , CaCl 2 , and NiCl 2 , m and n being numbers such that: ##EQU2##

The present invention relates to a process for producing cold bysolid-gas reaction.

The invention also relates to the device for implementing this process.

At present, plants for producing cold make use almost exclusively ofcompression cycle (compressor--condenser--expansion valve--evaporator).

The advantages of these plants lie chiefly in the fact that they makeuse of a very well known and proven technique, and make it possible toobtain a good performance (approximately 2 in air conditioning), 1.5 atabout 0° C., below 1 in the case of very low temperatures).

The disadvantages of these plants are linked with the presence of thecompressor, which presents problems of maintenance and, obviously, withthe need to have mechanical energy available (generally in electricform).

The absorption cycle is based on the affinity of one fluid for another.A cycle of this kind comprises an evaporator, an absorber, a separatorboiler, a condenser and an expansion valve.

In the case of low temperatures, the formula which is generally adoptedis the ammonia/water solution. The advantage of the absorption cycle isthat it requires only heat energy (waste heat, gas, lean gas etc.) andthat it does not employ essential mechanical parts.

The disadvantages of this cycle are: a relatively low performance (below0.5-0.8) and the fact that it demands the circulation of a largequantity of solution.

Other known devices for producing cold are gas expansion (airplaneair-conditioning), the Peltier effect, and solid sorption systems, whichare described hereinafter.

The solid-gas systems make use of adsorption or reaction phenomena. Theyinvolve chiefly the following systems:

the zeolite water (Z water) system, limited to a temperature above 0°C.,

the active carbon-methanol (AC-methanol) system

the hydride systems

the salt/ammonia or ammonia derivative systems.

The development of the first three systems above has encountered thefollowing difficulties:

low energy density (Z-water, AC-methanol)

rare products and the presence of hydrogen (hydrides)

system under very low pressure (Z-water)

difficulties of management in the case of divariant systems (Z-water, ACmethanol).

The development of salt/ammonia or derivative systems has long been heldback by the low powers obtained. Studies carried out on transfers (ofmass and of heat) and on kinetics-transfers couplings, have led to theinvestigation of a binder permitting these transfers to be improved.

The research carried out has made it possible to produce reactionmixtures which under certain conditions produce powers of several kW/kgof salt. This power level makes it possible to design systems whoseperformance is comparable to the conventional compression systemsemployed at present.

The basis of the system for producing cold by solid-gas reaction will berecalled below. Under given temperature and pressure conditions, certainsolids can react with certain gases: this reaction results in theformation of a defined, generally solid, chemical compound and isaccompanied by a heat release. When, under other temperature andpressure conditions, heat is introduced into the compound thus formed, agas release and the formation of the initial solid product are observed.

The operation of the system takes place, therefore, in two stages whichare offset in time, illustrated by FIG. 1, and explained below:

In the first stage, known as an "evaporation-synthesis stage",evaporation of a refrigerant fluid and reaction of the gas thus formedwith the solid take place simultaneously:

    [G] liq.→(G) gas

    <S>+(G)→<S, G>                                      (I)

The fluid F1 supplies the heat ΔHL to the evaporator E. The liquid [G]evaporates and the gas formed is fixed in the reactor R on the solid <S>to give the compound <S,G>. In the reactor R, the reaction isaccompanied by a release of heat ΔHR, the latter being removed by thefluid F2. The cold source is therefore the evaporator E, the cold beingused directly or indirectly starting with the fluid F1.

In the second stage, called a "decomposition - condensation stage",decomposition of the solid <S,G> takes place simultaneously with releaseof the gas (G), in the reactor R, and with condensation of (G) in thecondenser C:

    <S,G>→<S>+(G)

The heat ΔHR is contributed to the solid <S,G> contained in the reactorR by the fluid F3 (or the fluid F2 employed previously). Under theeffect of the heat, the gas (G) is released and condenses in C, thecondensation being accompanied by the release of heat ΔHL, the latterbeing removed by the fluid F4.

The thermodynamic characteristics of the system employed are as follows:

Since a true chemical reaction between a solid and a gas is present, amonovariant system at equilibrium is involved, that is to say that thereexists an unambiguous relationship between the temperature and pressure,of the form:

    Log P=A-B/T

in which expression P is the pressure, T the temperature (expressed indegrees K), A and B being constants characteristic of the solid/gas pairemployed.

The two stages of operation may be represented on a pressure/temperaturediagram, as shown in FIG. 2.

In this FIG. 2, (I) is the equilibrium (G)→>[G] and

    (J) is the equilibrium

    <S>+(G)→><S,G>

The equilibrium straight line (I) determines two regions in which eithercondensation or evaporation of the compound (G) takes place. Theequilibrium straight line (J) determines two regions in which there iseither synthesis of the compound <S,G> from <S> and from <G>, ordecomposition of the solid <S,G> with release of (G).

During the evaporation-synthesis stage, [G] evaporates at thetemperature TE and will react with the solid <S> which is at temperatureTA. This temperature TA is such that the operating point of the solid(point P) is in a synthesis region. This stage takes place at thepressure PB.

During the decomposition-condensation stage, the compound <S,G> is at atemperature TD such that the operating point of the solid (point Q) isin a decomposition region. The compound (G) which is released willcondense at the temperature TC. This stage takes place at the pressurePH such that PH is higher than PB.

None of the solid-gas reactions known at present makes it possible toproduce cold down to -40° C., the maximum temperature outside theenclosure being +30° C., and at the same time to produce cold down to+10° C., the maximum temperature outside the enclosure being +80° C.

A reaction which would make it possible to obtain these temperatureswould be particularly well adapted to the production of an industrialdevice for producing cold in vehicles for transporting products such asfoodstuffs which are deep-frozen or kept at low temperature.

The purpose of the present invention is precisely to achieve thisobjective.

The process to which the invention relates makes it possible to producecold by means of a device comprising a reactor which contains a solidcompound capable of reacting with a gas according to an exothermicreaction, this reactor being connected to a condenser, a gas collectorand an evaporator which is in a heat exchange relationship with anenclosure to be cooled, the interior of the reactor being in a heatexchange relationship with an external heat source.

According to the invention, a feature of this process is that thefollowing simultaneous reactions are produced in the reactor: ##EQU3##

X being chosen from ZnCl₂, CuSO₄, CuCl, LiBr, LiCl, ZnSO₄, SrCl₂, MnCl₂,FeCl₂, MgCl₂, CaC₂ and NiC₂, m and n being numbers such that: ##EQU4##

The symbols <>, [], ( ) above refer to a compound in the solid state, inthe liquid state and in the gaseous state, respectively.

Thus, if the intention is to produce cold down to -40° C. in theenclosure to be refrigerated, the maximum temperature outside the latterbeing not more than 30+ C., the distance of the point Q (FIG. 2)relative to the equilibrium straight line J being 20° C. and thecondensation temperature being 35° C., an external heat source isemployed, whose temperature is higher than a value T_(h) such that:##EQU5##

Furthermore, if the intention is to produce cold down to +10° C. in theenclosure to be refrigerated, the maximum temperature outside the latterbeing not more than +80° C., the distance of the point Q (FIG. 2)relative to the equilibrium straight line J being 20° C. and thecondensation temperature being 85° C., an external heat source isemployed, whose temperature is higher than a value T_(h) such that:##EQU6##

The invention also relates to a device for producing cold at atemperature of between -40° C. and +10° C., in which the process inaccordance with the invention is implemented.

Another aim of the invention is to create a device permitting cold to beproduced continuously.

According to the invention, this device comprises two reactorscontaining the same solid compound, communication circuits between thesereactors, the evaporator, the condenser and the gas collector, and meansare provided for successively triggering the solid-gas reactions in thetwo reactors and for producing the opening and closing of the variouscommunication circuits in a predetermined order, to obtain a continuousproduction of cold.

According to a preferred version of the invention, the abovementionedmeans are adapted to permit the following succesive steps of operation:

(A) opening of :ne circuit between one of the reactors and theevaporator and between the latter and the gas collector,

(B) opening of the circuit between the evaporator and the first reactoras soon as the gas pressure in the evaporator is higher than that in thefirst reactor,

(C) opening of the circuit between the other reactor and the evaporatorand between the latter and the gas collector,

(D) opening of the circuit between the evaporator and the second reactoras soon as the gas pressure in the evaporator is higher than that in thesecond reactor,

(E) opening of the circuit between the first reactor and the externalheat source to heat the solid contained in this reactor,

(F) opening of the circuit between the first reactor and the condenseras soon as the pressure in the reactor is higher than that in thecondenser,

(G) closing of the circuit between the first reactor and the heat sourceand opening of the circuit between the second reactor and the heatsource,

(H) closing, under the effect of the pressure prevailing in the secondreactor, of the circuit included between the latter and the evaporatorand opening of the circuit between the second reactor and the condenser,

(I) closing, after a pressure drop in the first reactor, of the circuitbetween the latter and the condenser and opening of the circuit betweenthis reactor and the evaporator.

According to an advantageous version of the invention, the devicecomprises a third reactor containing the said solid compound capable ofreacting with the gas and connected to the external heat source, thecondenser, the collector and the evaporator, means being provided forsuccessively starting the solid-gas reactions in the three reactors insuch a way that the third reactor can store energy without any energyinput other than that needed for the circulation of the heat transferfluid.

Other special features and advantages of the invention will becomeapparent again in the description below.

In the attached drawings, given by way of examples, without anylimitation being implied:

FIG. 1 is a schematic view illustrating the two successive stages of theprior art process for producing cold from a solid-gas system usingreaction phenomena;

FIG. 2 is a pressure versus temperature diagram illustrating theoperation of the prior art system of FIG. 1;

FIG. 3 is the diagram of a device for producing cold, with a singlereactor,

FIG. 4 is a diagram similar to FIG. 3, showing the first step of theoperation of the device according to FIG. 3,

FIG. 5 shows the second step of the operation of the device according toFIG. 3,

FIG. 6 shows the third step of the operation of the device according toFIG. 3,

FIG. 7 is the diagram of a device for producing cold, with two reactors,

FIG. 8 shows the first step of the operation of the device according toFIG. 7,

FIG. 9 shows the second step of the operation of the device according toFIG. 7,

FIG. 10 shows the third step of the operation of the device according toFIG. 7,

FIG. 11 shows the fourth step of the device according to FIG. 7,

FIG. 12 is the diagram of a device for producing cold, with threereactors,

FIG. 13 shows the first step of the operation of the device according toFIG. 12,

FIG. 14 shows the second step of the operation of the device accordingto FIG. 12,

FIG. 15 shows the third step of the operation of the device according toFIG. 12,

FIG. 16 shows the fourth step of the operation of the device accordingto FIG. 12.

Shown in the embodiment of FIG. 3 is a device for producing coldnoncontinuously from a physicochemical phenomenon by reacting manganesechloride with ammonia, as indicated below:

    <MnCl.sub.2, 2NH.sub.3 >+4(NH.sub.3) →<MnCl.sub.2, 6NH.sub.3 >

This device comprises:

a reactor R containing the solid reaction medium <MnCl₂, 2NH₃ > which isconnected to a condenser C, a collector Co for liquefied gas G comprisedbetween the latter and an evaporator E.

This device furthermore comprises a nonreturn valve C1 in the circuitconnecting the reactor R to the condenser C, a nonreturn valve C2 in thecircuit connecting the evaporator E to the reactor E, a thermostaticexpansion valve DT in the circuit connecting the reactor R to theevaporator E, a controlled pressure valve VPC, a solenoid valve EV1isolating the reactor R from the remainder of the circuit, a solenoidvalve EV2 isolating the evaporator E from the reactor R, two solenoidvalves EV3 and EV4 for defrosting and a solenoid valve EV5 permitting aheat transfer fluid F4 to be distributed into the exchanger EC containedin the reactor E and connected to an external heat source S by means ofa pump P.

The various steps of operation of the device are illustrated by FIGS. 4to 6 and by the table below:

                  TABLE 1                                                         ______________________________________                                        Stop         Start-ups                                                                              Cycle     Defrosting                                    Stages  0        0        1     2   3                                         ______________________________________                                        EV1     C        0        0     0   0                                         EV2     C        0        0     0   C                                         EV3     C        C        C     C   0                                         EV4     C        C        C     C   0                                         EV5     C        C        C     0   0                                         C1      C        C        C     0   0                                         C2      C        C        0     C   C                                         ______________________________________                                         *0 = open; C = closed                                                    

Initial state: step 0

The reactor R has a maximum cold potential, that is to say that thesolid within consist of salt <S> capable of reacting with the gas (G).

All the solenoid valves are closed and the collector Co is filled withrefrigerant fluid [G]. To start up, the solenoid valve EV1 is opened.

Step 1 (FIG. 4)

The solenoid valve EV2 opens, the fluid G travels from the condenser Ctowards the evaporator E. In the latter it vaporizes, the heat beinggiven up by the fluid F₂, for example air, which is employed forconveying the cold produced. The fluid F2 carries the negative caloriesthroughout the enclosure to be cooled. In the example shown, air isblown into this enclosure by means of a fan V1.

The thermostatic expansion valve (VPC) controls the pressure in theevaporator E and consequently the temperature of the liquid G boiling inthe evaporator E. When the pressure in the evaporator E is higher thanthe pressure in the reactor R, the valve C2 opens and the gas (G) reactswith the solid <S> in the reactor R, the heat of reaction being removedby means of an exchanger where F3 circulates. The fluid F3 is airpropelled by a motor-driven fan V3 which removes the heat of exothermicreaction to the outside.

Step 2 (FIG. 5)

When the synthesis reaction has ended in the reactor R, the valve EV5opens, the solid <S,G> present in the reactor R is heated by the fluidF4 which is, for example, a thermal oil. When the pressure in thereactor R is higher than that prevailing in the condenser C, or in thecollector Co, the valve C1 opens, the valve C2 having closed as soon asthe pressure in the reactor R was higher than that prevailing in theevaporator E.

The gas originating from the reactor R condenses in the condenser C andthen flows into the collector Co, the heat of condensation being removedby the fluid F1, the fluid F1 being air, as in a traditional compressionplant, blown in by means of a fan V2.

During this step 2 no cold production takes place, since the fluid [G]cannot circulate in the evaporator. The production of cold is thereforenoncontinuous.

Step 3 (FIG. 6)

This step, when forming part of the cycle, corresponds to defrosting.The latter takes place within the evaporator E itself, employing it as acondenser.

The initiation of the defrosting operation must take place during step2, that is to say during the operation of the composition of the solidin the reactor R.

For this operation, the valve EV2 closes and the valve EV3 opens,simultaneously.

The gas (G) originating from the decomposition reaction in the reactor Rcondenses preferentially in the evaporator E and thus produces thedefrosting. Since the valve EV4 is open, the condensed fluid [G] flowsinto the collector Co.

Step 4

In this step, step 1, that is to say the production of cold by theevaporator E, recommences.

The device just described, although producing cold noncontinuously,makes it possible to produce cold down to -40° C. in the enclosure to berefrigerated, on condition that the maximum temperature outside thelatter does not exceed 30° C.

To this end, it is necessary:

(1) to produce the following simultaneous reactions inside the reactorR: ##EQU7##

X being chosen from ZnCl², CuSO₄, CuCl, LiBr, LiCl, ZnSO₄, SrCl₂ MnCl₂,FeCl₂, MgCl₂, CaCl₂ and NiCl₂, m and n being numbers such that: ##EQU8##

(2) that the external heat source S is at a temperature T_(h) higherthan a value such that: ##EQU9##

If the intention is to produce cold down to +10° C. in the enclosure tobe refrigerated, the maximum temperature outside the latter being notmore than +80° C., with the aid of the same solid-gas reactions, thetemperature T_(h) of the source S will need to be higher than a valuesuch that: ##EQU10##

It is possible, therefore, with the aid of the same single reactionchosen from the reactions above and using a heat source S whosetemperature is at the appropriate value, to provide cold at atemperature of between +10° C. and -40° C.

The devices for producing cold which will now be described make itpossible, furthermore, to produce cold continuously, which makes themparticularly suited to industrial needs, especially in transportvehicles.

The device shown in FIG. 7 comprises chiefly:

two identical reactors (R1 and R2) containing the solid reaction medium,

a condenser C,

a collector Co for liquefied gas G,

an evaporator E,

two nonreturn valves (C1 and C2) in the circuits connecting the reactorsR1 and R2 to the condenser C,

two nonreturn valves (C3 and C4) in the circuits connecting theevaporator E to the reactors R1 and R2,

a thermostatic expansion valve (DT) between the evaporator E and thecollector Co,

a controlled pressure valve (VPC) between the reactors R1, R2 and theevaporator E,

two solenoid valves (EV1 and EV2) isolating the reactors R1 and R2 fromthe remainder of the circuit,

a solenoid valve (EV5) isolating the evaporator E from the reactors R1and R2,

two solenoid valves (EV6 and EV7) for defrosting,

two solenoid valves (EV3 and EV4) permitting a fluid F4 to bedistributed into the exchangers EC1 and EC2 contained in the reactors R1and R2.

The various steps of operation of this device are illustrated by FIGS. 8to 11 and by the table 2 below.

                  TABLE 2                                                         ______________________________________                                        Start up      Cycle     Defrosting* Recharge                                  Stages 0     1        2   3     4    5      6                                 ______________________________________                                        EV1    C     0        0   0     0    0      0                                 EV2    C     C        0   0     0    0      0                                 EV3    C     C        0   C     C    C      0                                 EV4    C     C        C   0     0    0      0                                 EV5    C     0        0   0     C    0      0                                 EV6    C     C        C   C     0    C      C                                 EV7    C     C        C   C     0    C      C                                 F3 to  --    R1       R2  R1    R1   R1                                       C1     C     C        0   C     C    C      0                                 C2     C     C        C   0     0    0      0                                 C3     C     0        C   0     C    0      C                                 C4     C     C        0   C     C    C      C                                 ______________________________________                                         *case where the defrosting takes place during step 3                     

Initial state: Step 0

The reactors R1 and R2 have a maximum cold potential, that is to saythat the solid within consist of salt <S> capable of reacting with thegas (G). All the solenoid valves are closed and the collector Co isfilled with refrigerant fluid.

Step 1: (FIG. 8)

The solenoid valves EV1 and EV5 open. The fluid G travels from thecollector Co towards the evaporator E. It vaporizes in the latter, theheat being given up by the fluid F2 which is therefore employed forproducing cold.

Since fluid F2 is air, it carries the negative calories into theenclosure to be cooled.

The thermostatic expansion valve (DT) prevents the fluid F fromtravelling in the liquid state beyond the evaporator E. The valve VPCcontrols the evaporation pressure level and hence the evaporationtemperature. When the pressure in the evaporator E is higher than thepressure in the reactor R1, the valve C3 opens and the gas (G) reactswith the solid <S> in R1, the heat of reaction being removed by means ofan exchanger where F3 circulates. The fluid F3 is air propelled by amotor-driven fan V3 which removes the heat of exothermic reaction to theoutside.

Step 2: (FIG. 9)

When the synthesis reaction has ended in the reactor R1, the valve EV2opens. When the pressure in the evaporator E is higher than the pressureprevailing in the reactor R2, the valve C4 opens and the fluid Gevaporates in the evaporator E and will react with the solid <S> presentin the reactor R2.

The heat of evaporation is introduced into the evaporator E by the fluidF2 and the heat of reaction released in R2 is removed by the fluid F3.

Simultaneously with the opening of the valve EV2, opening of the valveEV3 takes place. The solid <S,G> present in the reactor R1 is heated bythe fluid F4. When the pressure in the reactor R1 is higher than thatprevailing in the condenser C (or in the collector Co), the valve C1opens, the valve C3 having closed as soon as the pressure in R1 washigher than that prevailing in the evaporator E.

The gas (G) originating from the reactors R1 condenses in the condenserCo, the heat of condensation being removed by the fluid F1, and flowsinto the collector Co.

Step 3: (FIG. 10)

When the reactions in the reactors R1 and R2 have ended, the valve EV3closes and the valve EV4 opens. The solid <S,G>present in R2 is heatedby the fluid F4. The pressure in R2 rises and, successively, the valveC4 closes and the valve C2 opens. The gas (G) originating from R2condenses in E, the heat of condensation being removed by the fluid F1,and flows into the collector Co.

The fluid F3 circulates in the exchanger E of the reactor R1. As thelatter cools, the pressure drops and, successively, the valve C1 closesand the valve C3 opens. The fluid (G) evaporates in E and reacts in thereactor R1 with the solid <S>. The heat of evaporation is, as before,provided by the fluid F2 (air) which cools and which is thereforeemployed for distributing cold in the enclosure to be cooled.

Step 4: (FIG. 11)

This step, which can intervene during step 2 or 3, refers to thedefrosting operation. The latter takes place within the evaporator Eitself, employing it as a condenser.

When the defrosting is started, the valve EV5 closes and the valve EV6opens.

The gas (G) originating from the decomposition reaction condensespreferentially in the evaporator E.

The heat of condensation which is released provides the defrosting.Since the valve EV7 is open, the condensed fluid G flows into thecollector Co.

Step 5:

This step corresponds to the return to the normal cycle after thedefrosting operation. The valves EV6 and EV7 close and EV5 opens.

The gas (G) travels from the reactor R1, heated by the fluid F4, towardsthe condenser C and the collector Co.

The gas (G) evaporates in E and reacts with the solid <S> in the reactorcooled by the fluid F3. As described in step 2 or 3, the cycle normallyrecommences by alternating steps 2 or 3.

Step 6:

This step does not correspond to the normal operating cycle, but itmakes it possible to restore to the machine its whole refrigeratingpotential (step 0).

During this step no production of cold takes place and the two reactorsR1 and R2 are restored to their maximum cold potential.

The valves EV3 and EV4 are open.

The solid (S,G> present in the reactors R1 and R2 is heated by the fluidF4.

The gas (G) produced during the decomposition of <S,G> condenses in Cand flows into the collector Co. The operation ends when only solid <S>is left in each of the reactors R1 and R2. The valves EV1 to EV5 arethen closed, the valves C1 and C2 closing as a result of the pressuredrop in R1 and R2, the latter being a consequence of the heating of thereactors being stopped.

When employing the solid-gas reactions described previously, the abovedevice makes it possible not only to produce cold continuously, but alsoto obtain temperatures between -40° C. and +10° C., which are an optimumfor the low-temperature transport of foodstuffs or other products.

FIG. 12 shows a device for producing cold, permitting, by starting witha noncontinuous physicochemical phenomenon, to ensure a continuousproduction of cold and a storage of refrigeration energy.

This device comprises mainly:

three identical reactors (R1, R2, R3) containing the solid reactionmedium,

a condenser C,

a collector Co for liquefied gas G,

an evaporator E,

three nonreturn valves (C1, C2, C3) in the circuit connecting thereactors R1, R2, R3 to the condenser C,

three nonreturn valves (C4, C5, C6) connecting the evaporator E to thereactors R1, R2, R3,

a thermostatic expansion valve (DT) between the evaporator E and thecollector Co,

three solenoid valves (EV1, EV2, EV3) isolating the reactors R1, R2 andR3 from the remainder of the circuit,

three solenoid valves (EV4, EV5, EV6) permitting a fluid F4 to bedistributed into the exchangers (EC1, EC2, EC3) contained in thereactors R1, R2, R3.

The various steps of operation of this device are shown in FIGS. 13 to16 and in the table 3 below.

                  TABLE 3                                                         ______________________________________                                                   Cycle                                                              Steps 0        1     2      3   4      5   6                                  ______________________________________                                        EV1   C        0     0      0   C      0   0                                  EV2   C        C     0      0   C      0   0                                  EV3   C        C     C      C   0      C   0                                  EV4   C        C     0      C   C      C   0                                  EV5   C        C     C      0   C      0   0                                  EV6   C        C     C      C   C      C   0                                  F3 to --       R1    R2     R1  R3     R1                                     C1    C        C     0      C   C      C   0                                  C2    C        C     C      0   C      0   0                                  C3    C        C     C      C   C      C   0                                  C4    C        0     C      0   C      0   C                                  C5    C        C     0      C   C      C   C                                  C6    C        C     C      C   0      C   C                                  ______________________________________                                    

Step 0: initial state

The reactors R1, R2 and R3 have maximum cold potential, that is to saythat the solids within consist of the salt <S> capable of reacting withthe gas (G). All the solenoid valves are closed and the collector Co isfilled with refrigerant fluid [G].

Step 1: start-up (FIG. 13)

The solenoid valve EV1 opens. The fluid G travels from the collector Cotowards the evaporator E. In the latter it evaporates, the heat beinggiven up by the fluid F2 which is employed for distributing the cold.The thermostatic expansion valve (DT) prevents the fluid [G] fromcirculating in the liquid state, beyond the evaporator E. When thepressure in the evaporator is higher than the pressure in R1, the valveC4 opens and the gas G reacts with the solid <S> in the reactor R1, theheat of reaction being removed by means of an exchanger where F3circulates.

Step 2: cycle (stage 1) (FIG. 14)

When the synthesis reaction has ended in the reactor R1, the valve EV2opens. When the pressure in the evaporator E is higher than the pressureprevailing in the reactor R2, the valve C5 opens and the fluid [G],which evaporates in E, reacts with the solid <S> present in the reactorR2.

The heat of evaporation is contributed to the evaporator E by the fluidF2 and the heat of reaction released in R2 is removed by the fluid F3.

Simultaneously with the opening of the valve EV2, opening of the valveEV4 takes place: the solid <S,G> present in the reactor R1 is heated bythe fluid F4. When the pressure in R1 is higher than that prevailing inthe condenser C (or in the collector), the valve C1 opens, the valve C4having closed as soon as the pressure in R1 was higher than thatprevailing in the evaporator E. The gas (G) originating from R1 iscondensed in the condenser C by the fluid F1 and flows into thecollector Co.

Step 3: cycle (stage 2) (FIG. 15)

When the reactions in the reactors R1 and R2 have ended, the valve EV4closes and the valve EV5 opens. The solid <S,G> present in R2 is heatedby the fluid F4. The pressure in R2 rises and, successively, the valveC5 closes and the valve C2 opens. The gas (G) originating from R2condenses in the condenser C, the heat of condensation being removed bythe fluid F1, and flows into the collector Co. The fluid F3 circulatesin the exchanger in the evaporator E of the reactor R1. As the lattercools, the pressure drops and, successively, the valve C1 closes and thevalve C4 opens. The fluid (G) evaporated in the evaporator E reacts inthe reactor R1 with the solid <S>. The heat of evaporation is, aspreviously, contributed by fluid F2, which cools and which is thereforeemployed for producing cold.

Alternation of stages 1 and 2 forms the normal operating cycle of thesystem.

Step 4: operation on storage (FIG. 16)

The fluid F4 is not heated and no longer circulates in the reactor R2.The circulation of (G), from R2 towards the condenser C, is stopped bythe closing of the valve EV2.

The fluid F3 no longer circulates in the reactor R1, the circulation of(G) from the evaporator towards the reactor R1 is stopped by the closingof the valve EV1.

The solenoid valve EV3 is open and the fluid F3 circulates in anexchanger EC3 situated in the reactor R3. When the pressure in theevaporator E is higher than the pressure prevailing in R3, the valve C6opens and the fluid (G) evaporated in E reacts with the solid <S> in R3;the heat of reaction is removed by F3 and the cold is conveyed by thefluid F2 cooled in the evaporator E.

Step 5: recommencement of the cycle (stage 2)

When the operation on storage is stopped, the normal cycle recommencesat step 3 (cycle: stage 2). The valve EV3 is closed and the valves EV1and EV2 are reopened. The fluid F4 is heated and circulates again in thereactor R2. The operation is then identical with that described in step3.

Step 6: recharge

This step corresponds to the stoppage of the cycle and to the restoringof the whole system to the initial state.

The valves EV1, EV2 and EV3 are open. The valves EV4, EV5 and EV6 beingopen, the fluid F4 circulates in the three reactors R1, R2 and R3. Thesolids inside these are heated: when the pressure in R1, R2 and R3 ishigher than the pressure prevailing in the condenser, the valves C1, C2and C3 open and the gas (G), originating from the decompositions of<S,G> condenses in the condenser and flows towards the collector Co. Theheat of condensation is removed by the fluid F1.

This operation is continued until the reactors contain only the solid<S>, that is to say until the step 0 (initial state) is regained.

As described with reference to the device with two reactors, thetechniques employed for controlling temperatures (VPC) and fordefrosting may be applied to this device with three reactors.

From the abovementioned description it follows that the third reactor R3enables energy to be stored without an energy input other than thatneeded to circulate the heat-transfer fluid F4.

Naturally, the invention is not limited to the examples of embodimentwhich have just been described and many modifications can be made to thelatter without departing from the scope of the invention.

Thus, the heat source S employed to heat the reactors R, R1, R2, R3 maybe any other heat source of thermal or electric origin which isavailable, provided that it is at the required temperature T_(h).

The fluid F4 may be any heat-transfer fluid other than oil.

Furthermore, the fluids F1, F2, F3 may be other than air.

Naturally, the process and the device in accordance with the inventionmay also be applied to the air conditioning of buildings, particularlyof dwellings.

I claim:
 1. A method for producing cold by means of a device comprisingat least a reactor (R, R1, R2, R3) which contains a solid compoundcapable of reacting with a gas according to an exothermic reaction, thisreactor being connected via one single isolation valve by separatecircuits to a condenser (C) and an evaporator (E) which is in a heatexchange relationship with an enclosure to be cooled, the condenser (C)and the evaporator (E) being respectively connected by separate lines toa gas collector (Co), the interior of the reactor being in a heatexchange relationship with an external heat source (S), wherein thefollowing simultaneous reactions are carried out in the reactor (R, R1,R2, R3): ##EQU11## the symbols <>, [ ] and ( ) denoting the sold, liquidand gaseous states respectively,X being chosen from ZnCl₂, CuSO₄, CuCl,LiBr, LiCl, ZnSO₄, SrCl₂, MnCl₂, FeCl₂, MgCl₂, CaCl₂ and NiCl₂, andwherein, for the purpose of producing cold down to -40° C. in theenclosure to be refrigerated, the maximum temperature outside the latterbeing not more than 30° C., an external heat source (S) is employed,whose temperature is higher than a value Th, m and n being integers andTh having a value such that: for: ##EQU12##
 2. A method for producingcold by means of a device comprising at least a reactor (R, R1, R2, R3)which contains a solid compound capable of reacting with a gas accordingto an exothermic reaction, this reactor being connected via one singleisolation valve by separate circuits to a condenser (C) and anevaporator (E) which is in a heat exchange relationship with anenclosure to be cooled, the condenser (C) and the evaporator (E) beingrespectively connected by separate lines to a gas collector (Co), theinterior of the reactor being in a heat exchange relationship with anexternal heat source (S), wherein the following simultaneous reactionsare carried out in the reactor (R, R1, R2, R3): ##EQU13## the symbols<>, [ ] and ( ) denoting the solid, liquid and gaseous statesrespectively,X being chosen from ZnCl₂, CuSO₄, CuCl, LiBr, LiCl, ZnSO₄,SrCl₂, MnCl₂, FeCl₂, MgCl₂, CaCl₂ and NiCl₂,and wherein, for the purposeof producing cold down to +10° C. in the enclosure to be refrigerated,the maximum temperature outside the latter being not more than +80° C.,an external heat source (S) is employed, whose temperature is higherthan a value Th, m and n being integers and Th having a value such that:for ##EQU14##
 3. The method as claimed in claim 1, the device comprisingtwo reactors (R1, R2) containing the same solid compound, communicationcircuits between these reactors, the evaporator (E), the condenser (C)and the gas collector (Co), wherein the solid-gas reactions aresuccessively started in the two reactors and the openings and closingsof the various communication circuits are produced in a predeterminedorder to obtain a continuous production of cold.
 4. The method asclaimed in claim 3, which comprises the following successive steps:(A)opening of the circuit between one (R1) of the reactors and theevaporator (E) and between the latter and the gas collector (Co), (B)opening of the circuit between the evaporator (E) and the reactor (R1)as soon as the gas pressure in the evaporator (E) is higher than that inthe reactor (R1), (C) opening of the circuit between the other reactor(R2) and the evaporator (E) and between the latter and the gas collector(Co), (D) opening of the circuit between the evaporator (E) and thereactor (R2) as soon as the gas pressure in the evaporator (E) is higherthan that in the reactor (R2), (E) opening of the circuit between thereactor (R1) and the external heat source (S) to heat the solidcontained in this reactor, (F) opening of the circuit between thereactor (R1) and the condenser (C) as soon as the pressure in thereactor is higher than that in the condenser, (G) closing of the circuitbetween the reactor (R1) and the heat source (S) and the opening of thecircuit between the reactor (R2) and the heat source (S), (H) closing,under the effect of pressure prevailing in the reactor (R2), of thecircuit included between the latter and the evaporator (E) and openingof the circuit between the reactor (R2) and the condenser (C), (I)closing, after a pressure drop in the reactor (R1), of the circuitbetween the latter and the condenser (C) and opening of the circuitbetween this reactor (R1) and the evaporator (E).
 5. The method asclaimed in claim 4, which comprises the step of triggering defrosting,said step including the following operations:closing of the circuitbetween the two reactors (R1) and (R2), opening of the circuit betweenthe evaporator (E) and the condenser (C) and opening of the circuitbetween the evaporator (E) and the gas collector (Co).
 6. The method asclaimed in claim 5, which comprises, after defrosting, the followingoperations:closing of the circuits between the evaporator (E) and thecondenser (C) and between the evaporator (E) and the gas collector (Co).7. The method as claimed in claim 3, further comprising the step ofcontrolling the pressure and the temperature of gas evaporation.
 8. Themethod as claimed in claim 3, further comprising the step of preventingthe fluid condensed in the condenser (C) from circulating in the liquidstate beyond the evaporator (E).
 9. The method as claimed in claim 3,the device comprising a third reactor (R3) containing the said solidcompound capable of reacting with the gas and connected to the externalheat source (S), the condenser (C), the collector (Co) and theevaporator (E), wherein the solid-gas reactions are successively startedin the three reactors (R1, R2, R3) so that the third reactor (R3) canstore energy without an energy input other than that needed for thecirculation of the heat-transfer fluid (F4).
 10. The method as claimedin claim 9, comprising the following successive operating steps:(A)opening of the circuit between the first reactor (R1) and the evaporator(E) and between the latter and the collector (Co), (B) opening of thecircuit between this reactor (R1) and the condenser (C), between thesecond reactor (R2) and the evaporator (E) and between the collector(Co) and the condenser (C), (C) opening of the circuit between the firstreactor (R1) and the evaporator (E), between the second reactor (R2) andthe condenser (C) and between the latter and the collector (Co), (D)opening of the circuit between the third reactor (R3) and the evaporator(E) and between the latter and the collector (Co).
 11. The method asclaimed in claim 2, the device comprising two reactors (R1, R2)containing the same solid compound, communication circuits between thesereactors, the evaporator (E), the condenser (C) and the gas collector(Co), wherein the solid-gas reactions are successively started in thetwo reactors and the openings and closings of the various communicationcircuits are produced in a predetermined order to obtain a continuousproduction of cold.
 12. The method as claimed in claim 11, whichcomprises the following successive steps:(A) opening of the circuitbetween one (R1) of the reactors and the evaporator (E) and between thelatter and the gas collector (Co), (B) opening of the circuit betweenthe evaporator (E) and the reactor (R1) as soon as the gas pressure inthe evaporator (E) is higher than that in the reactor (R1), (C) openingof the circuit between the other reactor (R2) and the evaporator (E) andbetween the latter and the gas collector (Co), (D) opening of thecircuit between the evaporator (E) and the reactor (R2) as soon as thegas pressure in the evaporator (E) is higher than that in the reactor(R2), (E) opening of the circuit between the reactor (R1) and theexternal heat source (S) to heat the solid contained in this reactor,(F) opening of the circuit between the reactor (R1) and the condenser(C) as soon as the pressure in the reactor is higher than that in thecondenser, (G) closing of the circuit between the reactor (R1) and theheat source (S) and opening of the circuit between the reactor (R2) andthe heat source (S), (H) closing, under the effect of pressureprevailing in the reactor (R2), of the circuit included between thelatter and the evaporator (E) and opening of the circuit between thereactor (R2) and the condenser (C), (I) closing, after a pressure dropin the reactor (R1), of the circuit between the latter and the condenser(C) and opening of the circuit between this reactor (R1) and theevaporator (E).
 13. The method as claimed in claim 12, which comprisesthe step of triggering defrosting, said step including the followingoperations:closing of the circuit between the two reactors (R1) and(R2), opening of the circuit between the evaporator (E) and thecondenser (C) and opening of the circuit between the evaporator (E) andthe gas collector (Co).
 14. The method as claimed in claim 13, whichcomprises, after defrosting, the following operations:closing of thecircuits between the evaporator (E) and the condenser (C) and betweenthe evaporator (E) and the gas collector (Co).
 15. The method as claimedin claim 11, further comprising the step of controlling the pressure andthe temperature of gas evaporation.
 16. The method as claimed in claim11, further comprising the step of preventing the fluid condensed in thecondenser (C) from circulating in the liquid state beyond the evaporator(E).
 17. The method as claimed in claim 11, the device comprising athird reactor (R3) containing the said solid compound capable ofreacting with the gas and connected to the external heat source (S), thecondenser (C), the collector (Co) and the evaporator (E), wherein thesolid-gas reactions are successively started in the three reactors (R1,R2, R3) so that the third reactor (R3) can store energy without anenergy input other than that needed for the circulation of theheat-transfer fluid (F4).
 18. The method as claimed in claim 17,comprising the following successive operating steps:(A) opening of thecircuit between the first reactor (R1) and the evaporator (E) andbetween the latter and the collector (Co), (B) opening of the circuitbetween this reactor (R1) and the condenser (C), between the secondreactor (R2) and the evaporator (E) and between the collector (Co) andthe condenser (C), (C) opening of the circuit between the first reactor(R1) and the evaporator (E), between the second reactor (R2) and thecondenser (C) and between the latter and the collector (Co), (D) openingof the circuit between the third reactor (R3) and the evaporator (E) andbetween the latter and the collector (Co).